In the administration of respiratory therapy or in respiratory treatment, particularly such as in the administration of inhalation therapy, a breathable gas such as, for example, air or oxygen, or a mixture of breathable gases such as, for example, a mixture of air, oxygen and helium, are administered to a patient to assist the patient in breathing. Such treatment is used for treating emphysema or asthma and other lung and respiratory diseases, as well as for postoperative treatment and cardiac patient care. During such treatment it is desirable to add moisture to the treating gas so as to prevent desiccation of the respiratory tract or membranes during treatment, especially over a long period of time. To this end moisture is added to the breathable gas or gases which results in the humidification of the breathable gases.
During the administration of such humidified respiratory gases, if the gas supply to a patient becomes partially blocked, or totally occluded, pressure increases in the humidified gas supply system. Such a pressure increase or blockage can reduce or stop the administration of the inhalation therapy to the patient, and if the pressure increases sufficiently a rupture of the humidified gas supply system can occur. Accordingly, it is desirable that the humidified respiratory gas supply system include a pressure relief system to guard against pressure build-up to a level which can cause a rupture in the humidified gas supply system, and that the pressure relief system include an alarm so that a healthcare provider or clinician will be alerted to this condition.
While provisions for pressure relief and audible signals to indicate a blockage in a humidified gas supply system are known to those skilled in the art, many such devices require high respiratory gas flow rates to cause a reliable audible tone to be generated. Such devices are unsuitable for use in a low flow humidified gas supply system wherein it is intended that the humidified respiratory gases be administered at a flow rate of between about 0.5 liters per minute to about 15 liters per minute such as used, for example, for neonatal patients. At such low flow rates such known devices do not reliably generate an audible tone to alert a clinician that a blockage has occurred.